1. Field of the Invention
The present invention relates generally to digital modality modeling, such as tomosynthesis, and in particular to classifying bone types prior to dental and orthopedic procedures.
2. Description of the Related Art
The field of dental diagnostics is generally concerned with locating pathologies in the dental structure, i.e. the teeth and the surrounding tissue and bone. Some of the more common pathologies are: 1) caries associated with decay; 2) fractures; 3) apical abscesses; and 4) morphologies of pulpal chambers and canals. The system and method of the present invention are primarily, but not exclusively, concerned with detecting these pathologies and with orthopedics.
Early detection of dental pathologies is very important in minimizing damage. Conventional diagnosis procedures are generally performed using dental X-rays (both fixed beam and scanning beam), explorers, and other conventional equipment.
Incipient caries, particularly those located within the enamel surface, often go undetected with conventional equipment. When such caries are finally found, considerable damage to tooth structure may have already occurred. Subsurface, incipient caries are located entirely within the enamel layer of the teeth. They are particularly difficult to locate using conventional diagnostic equipment and procedures. By the time such incipient caries are located, the extent of the damage is often 17% to 23% greater than it would appear to be on a conventional X-ray negative.
Dental fractures can result from bruxism (teeth grinding), trauma, etc. The dental structure that has been weakened by various causes, such as decalcification, is particularly susceptible to fractures. Fractures can assume various configurations, including “craze”, vertical, oblique and horizontal line patterns. Fracture patterns and configurations can be particularly difficult to locate using conventional X-ray equipment and procedures. For example, fractures which are generally parallel to the X-ray beam are often undetectable on an X-ray negative. Undetected, and hence untreated, fractures can provide direct paths through the enamel layer of the teeth whereby bacteria can invade the dentin and pulp layers. Pathologies in the dentin and pulp layers are often associated with considerable pain and tooth loss.
Apical abscesses comprise yet another dental condition which can be difficult to diagnose with conventional equipment, particularly in the early stages. Advanced apical abscesses can cause considerable pain because they involve the neurovascular bundles located in the root canals as well as the osseous tissue around the apex of the root. Early detection of apical abscesses can lead to appropriate, early-stage treatment, thus avoiding advanced disease processes with resultant pain, swelling, and other serious health consequences and complications.
Tomography or sectional radiography techniques using scanning X-ray beams have previously been employed for dental applications. For example, U.S. Pat. Nos. 4,188,537; 4,259,583; 4,823,369; 4,856,038; and 5,214,686 all relate to dental X-ray diagnosis utilizing scanning techniques and are incorporated herein by reference.
In the medical field, densitometry procedures are used for measuring bone morphology density (BMD) by utilizing scanning X-ray beam techniques. Examples are shown in U.S. Pat. Nos. 5,533,080; 5,838,765; and Re. 36,162, which are incorporated herein by reference. Medical applications of densitometry include the diagnosis and treatment of such bone diseases as osteoporosis. Dual energy x-ray absorptiometry (DEXA) utilizes x-rays with different peak energy levels for distinguishing soft and hard (e.g., muscle and skeletal) tissue structures based on their absorption of the x-rays at different energy levels.
The availability of relatively fast computers with large memories at reasonable costs has led to the digitalization of X-ray images for mapping BMD models in various formats. For example, BMD images use color to identify varying densities. Digital BMD patient models are also used for comparison purposes with standard models and with patients' own prior BMD histories. Age correction factors can be applied to patients' models for diagnosing and monitoring the onset and progress of such medical conditions as osteoporosis and the like. The present invention utilizes such densitometry modeling and mapping techniques for dental applications.
In addition to pathology detection and diagnosis, the present invention has applications in monitoring osseointegration, which occurs at the interface between bone structures and prostheses, such as implants and replacement joints. For example, dental implants osseointegrate with patients' dental structure. The application of tomographical densitometry techniques to osseointegration monitoring can provide the dental or medical practitioner with important information in evaluating the effectiveness of implant procedures.
Digital tomosynthesis utilizes computers for digitizing tomographic densitometry data and constructing 3-D models of patient and prosthetic regions of interest (ROIs). Using digital tomosynthesis techniques, partial rotation of source/receptor units and relatively few discrete exposures can produce sufficient information to construct 3-D models. By digitally processing the resulting images, tomographic slices at different depths and with different thicknesses can be reconstructed from individual data acquisitions, thus minimizing radiation exposure and procedure time. Digital tomosynthesis techniques have been utilized in mammography applications. The resulting 3-D digital tomosynthesis models are utilized for diagnostic, treatment, forensic and related purposes.
Other modeling and imaging modalities include computerized tomography (CT), magnetic resonance imaging (MRI), ultrasound, sonar, Doppler effect, photon emission tomography (PET) and single photon emission computed tomography (SPECT) scanning. The present invention is adapted for medical and dental applications involving the acquisition of signals, which are digitized and further processed to produce 3-D models corresponding to patient regions of interest (ROIs) including both hard and soft tissue structures and prosthetics.
Implants and other prostheses are used extensively in connection with treating a wide variety of dental and orthopedic conditions. The success of such implants commonly depends on the osseointegration of the implants, i.e. the extent of direct, structural and functional connection between ordered living bone and the surface of the implant. Osseo integration is directly related to endogenous factors such has bone quality and quantity. Radiographic diagnosis and resistance to cutting and drilling are generally accepted as the criteria for classifying bone quality as follows:
Type 1 comprising substantially entirely homogenous compact bone;
Type 2 comprising a thick layer of compact bone surrounding core of dense bone;
Type 3 comprising a thin layer of cortical bone surrounding a core of tents trabecular bone; and
Type 4 comprising a thin layer of cortical bone surrounding a core of low density, weak trabecular bone.
Classifying bone types has involved a wide variety of imaging procedures, such as radiography, computerized tomography (CT), magnetic resonance imaging (MRI) and ultrasound. Each has certain advantages and disadvantages. Dual energy x-ray absorptiometry (DEXA) is widely used, particularly for determining bone mass density (BMD) for diagnosing osteoporosis and other conditions, and for assessing fracture risks. Bone density normally varies with such factors as age and gender. DEXA test results are commonly reported as a combination of: measured density (g/cm3); Z-score (standard deviations above or below the mean for the patient's age and gender); and T-score (standard deviations above or below the mean for a healthy 30-year-old adult of the same gender). Based on such information, susceptibility to fracturing and prosthesis osseo-integration can be predicted. However, additional information and analysis would be useful to the health-care practitioner, particularly in connection with prosthetic implant procedures.
Heretofore there has not been available a system or method for applying digital tomosynthesis and related modalities for classifying bone densities, e.g., prior to dental and orthopedic procedures, with the advantages and features of the present invention.